1. Field of the Invention
The invention concerns a drive arrangement comprising a collectorless d.c. motor and an electrical commutation arrangement activated in dependence upon the angular position of the rotor of the motor, with steps being taken to keep commutation noise especially low.
2. Discussion of the Prior Art
Collectorless d.c. motors having an electrical commutation arrangement are well known.
In particular, from U.S. Pat. No. 4,230,976 of Rolf Mu/ ller there is known a drive arrangement having a collectorless d.c. motor having a permanent-magnet rotor and a stator winding arrangement. There are furthermore provided an angular-position transducer arrangement which during operation furnishes angular-position signals that are a function of the rotor's angular position, and an electrical commutation arrangement which receives the angular-position signals and selectively connects the stator winding arrangement to a current source. In the known arrangement the angular-position transducer is formed by a Hall generator. The Hall generator's operating current is modulated in synchronism with rotor rotation in such a manner that there occurs a decrease of the Hall generator's operating current when the flux density at the Hall generator is zero or almost zero. As a result the current flowing through the stator winding is substantially reduced or interrupted at about the times at which commutation is to occur.
In practice, however, for the control of the commutation of collectorless d.c. motors there are often employed angular-position transducers which permit no modulation of their operating current, in which event the technique known from the said U.S. Pat. No. 4,230,976 is accordingly ruled out to begin with. For example, Hall-IC arrangements belong to that type of angular-position transducers.
One object of the present invention is to provide a drive arrangement comprising a collectorless d.c. motor and an electrical commutation arrangement that runs particularly uniformly and in which noise attributable to the commutation is reduced in an effective way. The novel drive arrangement accordingly should be capable of being equipped with angular-position transducers of any type at all, e.g. even with Hall-IC arrangements.